Drive sprocket for a tracked vehicle

ABSTRACT

A snowmobile is propelled by an endless track that is operatively connected to the snowmobile&#39;s engine by two drive sprockets. Each drive sprocket includes one set of external teeth and two sets of internal teeth that engage three corresponding sets of track teeth formed on the track. Alignment cleats are mounted on the inside of each of one of the sets of track teeth. During low-load operation, contact between the cleats (and the track teeth on which the cleats are mounted) is minimized or eliminated, which reduces or eliminates noise caused by collisions between the metal sprocket and the metal cleats. During higher load operation, the track deforms such that the set of external sprocket teeth engage the cleats and associated set of track teeth.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. application Ser. No.10/636,917 filed on Aug. 8, 2003. Through the '917 application, thepresent application claims priority to US Provisional Application No.:60/402,088 filed on Aug. 9, 2002. The disclosure of both areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to drive sprockets for trackedvehicles, and relates more specifically to the tooth design for suchdrive sprockets having improved traction with reduced noise generation.

2. Description of Related Art

Tracked vehicles such as snowmobiles and snow groomers drivingly engagethe ground through one or more endless tracks. Endless tracksconventionally include an outer side with a pattern of projecting lugsor ribs that are designed to engage the snow or other ground surface,apply traction, and propel the vehicle. Conventional endless tracks alsoinclude an inner side that engages one or more drive sprockets, which,in turn, are operatively connected to a propulsion system of thevehicle.

The drive sprockets and the inner side of the endless track typicallyinclude mating teeth that provide traction between the drive sprocketsand the endless track. Conventional drive sprockets use either externalor internal teeth.

FIGS. 9 and 10 illustrate a drive sprocket 1010 that includes aplurality of radially-extending sprocket teeth 1020 projecting outwardlyfrom an outer circumferential side of the sprocket 1010. An endlesstrack 1030 includes a plurality of longitudinally spaced holes thatdefine a plurality of track teeth 1040. Reinforcing metal bars (notshown) extend laterally across the endless track 1030 through the trackteeth 1040 to reinforce the track teeth 1040 and the track 1030. Thetrack teeth 1040 mesh with the sprocket teeth 1020 to provide tractionbetween the drive sprocket(s) 1010 and the track(s) 1030. In the typicalexample where the drive sprocket 1010 is used, two such sprockets 1010usually are provided to engage each endless track 1030.

Each track tooth 1040 is surrounded by a metal alignment cleat 1050 thatmeshes with the sprocket 1010 to keep the endless track 1030 laterallyaligned with the drive sprockets 1010. As the drive sprockets 1010rotate to propel the vehicle, the cleats 1050 rattle against the valleysformed between adjacent sprocket teeth 1020. This metal-to-metal contactcreates noise, especially when the vehicle travels quickly.

FIGS. 11-13 illustrate an additional conventional drive sprocket 1060that includes a plurality of axially-extending sprocket teeth 1070. Anendless track 1080 includes a plurality of longitudinally-spaced trackteeth 1090 projecting inwardly from an inner side of the endless track1080. The sprocket teeth 1070 engage the track teeth 1090 to providetraction between the sprocket 1060 and the endless track 1080. Alignmentcleats 1050 are laterally offset from the track teeth 1090 on theendless track 1080 and the sprocket teeth 1070. Consequently, the cleats1050 do not typically rattle against the sprockets 1060 as much as inthe previous example, and noise is reduced as compared to sprockets 1010that rely on radially-extending teeth 1020.

While the use of axially-extending teeth 1070 instead ofradially-extending teeth 1020 reduces noise, the axially-extending teeth1070 are not as effective at generating traction with the track 1080 asthe radially-extending teeth 1020. The reduction in traction may becaused, in part, by the fact that the internal track teeth 1090 aretypically not reinforced and therefore deform under high loads.Accordingly, a greater number of sprockets 1060 must be used to generatesufficient traction with the endless track 1080. As illustrated in FIGS.8 and 9, four internally toothed sprockets 1060 (two inner sprockets1060 with two sets of sprocket teeth 1070 and two outer sprockets 1060with one set of sprocket teeth 1070) are typically used.

As a result of this, a need has developed for a sprocket constructionthat provides the superior traction of the drive sprocket 1010 whilealso minimizing the generation of noise as does the drive sprocket 1030.

Others have attempted to solve these problems. FIGS. 14-16 illustrate anadditional conventional drive sprocket 1110 that includes a plurality ofaxially-extending sprocket teeth 1120. The sprocket teeth 1120 engagethe track teeth 1090 of the endless track 1080, as shown, for example,in FIGS. 12 and 13. The drive sprocket 1110 further includes a pluralityof radially-extending sprocket teeth 1130 projecting outwardly from thean outer circumferential side of the sprocket 1110. Theradially-extending sprocket teeth 1 130 mesh with track teeth 1040, asshown, for example in FIGS. 9 and 10 to provide traction between thedrive sprocket 1110 and the endless track. The radially-extendingsprocket teeth 1130 extend directly from the outer circumference of thesprocket 1110 and have a width substantially the same as the sprocketteeth 1120. The drive sprocket 1110 exhibits many of the drawbacksidentified above.

SUMMARY OF THE INVENTION

Accordingly, one aspect of embodiments of the present invention providesa drive sprocket that generates more traction than conventional drivesprockets.

An additional aspect of embodiments of the present invention provides animproved drive sprocket that reduces noise.

A further aspect of embodiments of the present invention provides animproved drive sprocket that includes at least two sets of teeth.

A further aspect of embodiments of the present invention provides adrive sprocket with both radially-extending and axially-extending teeth.

A further aspect of embodiments of the present invention provides asprocket for a vehicle having an endless track and a power plant. Thesprocket includes a sprocket wheel that is engagable with the powerplant of the vehicle. The sprocket wheel has a rotational axis, aperimetrical surface, and first and second axial surfaces. The sprocketalso includes a first plurality of teeth extending radially outwardlyfrom the perimetrical surface in spaced-apart relation, and at least asecond plurality of teeth extending axially outwardly from the firstaxial surface in spaced-apart relation. A third plurality of teeth canextend axially outwardly from the second axial surface in spaced-apartrelation.

The sprocket wheel, the first plurality of teeth, and the secondplurality of teeth may be integrally formed. The sprocket may alsoinclude a third plurality of teeth extending axially outwardly from thesecond axial surface in spaced-apart relation. Each of the firstplurality of teeth, each of the second plurality of teeth, and each ofthe third plurality of teeth may be radially aligned.

The perimetrical surface defines valleys between adjacent ones of thefirst plurality of teeth. The perimetrical surface may be generallycylindrically shaped such that each valley comprises an arc-shapedsurface.

Each of the second plurality of teeth define an outward surface that maybe disposed radially farther from the rotational axis than adjacentvalleys.

Each of the second plurality of teeth may have two notches therein. Eachof the second plurality of teeth has a base portion and a tip portion.The notches may be formed in the base portion.

In a circumferential direction, each of the second plurality of teethmay be wider than each of the first plurality of teeth.

Embodiments of the present invention are also directed toward a vehiclethat includes a frame, a power plant supported by the frame, and asprocket operatively connected to the power plant. The sprocket is oneof the previously described sprockets.

The endless track may include a belt having an outer side and an innerside. The belt has a plurality of holes therethrough. The portions ofthe belt between the holes define a first plurality of track teeth. Theendless track also includes a plurality of lugs projecting from theouter side, and a second plurality of track teeth projecting from theinner side. The second plurality of track teeth engage the secondplurality of sprocket teeth.

Each of the first plurality of track teeth may longitudinally registerwith each of the second plurality of track teeth, and each of the firstplurality of sprocket teeth may be radially aligned with each of thesecond plurality of sprocket teeth.

The endless track may further include a third plurality of track teethprojecting from the inner side. The third plurality of track teethengages the third plurality of sprocket teeth. Each of the second andthird pluralities of track teeth may be disposed laterally adjacent toeach of the first plurality of teeth, on opposite sides thereof. Each ofthe first plurality of sprocket teeth, each of the second plurality ofsprocket teeth, and each of third plurality of sprocket teeth may beradially aligned.

When the endless track does not deform, the first plurality of trackteeth preferably do not engage the perimetrical surface. Similarly, whenthe endless track does not deform, the first plurality of track teethpreferably do not engage the first plurality of sprocket teeth. Thesecond plurality of track teeth may include a flexible, resilientmaterial. When the second plurality of track teeth deform under a loadexerted thereon by the second plurality of sprocket teeth, the firstplurality of sprocket teeth may engage the first plurality of trackteeth to supplement traction between the sprocket and the endless track.

The endless track may further include a plurality of cleats. Each cleatincludes a base portion secured to one of the first plurality of trackteeth and at least one cleat portion projecting from the base portionaway from the inner side. When the second plurality of teeth do notdeform, the base portions of the cleats do not contact the perimetricalsurface. When the second plurality of track teeth deform under a loadexerted thereon by the second plurality of sprocket teeth, the firstplurality of sprocket teeth engage the cleats to enhance tractionbetween the sprocket and the endless track.

The perimetrical surface may define a sprocket valley between adjacentteeth of the first plurality of sprocket teeth. The inner side of thebelt may define a track valley between adjacent teeth of the secondplurality of track teeth. Each of the second plurality of sprocket teethdefines an outward surface, and the outward surfaces of the secondplurality of sprocket teeth engage the track valleys as the sprocketrotates such that when the endless track does not deform, the firstplurality of track teeth do not contact the sprocket valleys.

The endless track may further include a plurality of alignment cleats.When the endless track does not deform, the base portions of the cleatspreferably do not contact the sprocket valleys.

The endless track may be a resilient, flexible material. The first andsecond pluralities of track and sprocket teeth may be sized and spacedsuch that the first plurality of sprocket teeth drivingly engage thefirst plurality of track teeth only when a portion of the endless trackdeforms longitudinally as the second plurality of sprocket teeth apply aload thereto.

When the endless track is laterally aligned with the sprocket, the cleatportions of the cleats preferably do not touch the sprocket as thesprocket rotates. As the sprocket rotates, the cleat portions preferablyextend into the notches of adjacent ones of the second plurality ofsprocket teeth.

The first plurality of track teeth may engage the first plurality ofsprocket teeth as the sprocket rotates.

Embodiments of the present invention are also directed toward a sprocketfor a vehicle having an endless track and a power plant. The sprocketincludes a sprocket wheel engagable with the power plant of the vehicle.The sprocket wheel has a rotational axis. The sprocket also includes atleast first and second pluralities of sprocket teeth projectingoutwardly from the sprocket wheel.

Embodiments of the present invention are also directed toward a vehiclethat includes a frame, a power plant supported by the frame, and atleast one sprocket operatively connected to the power plant. Each of theat least one sprockets includes a sprocket wheel rotationally supportedby the frame and operatively connected to the power plant. Each sprocketalso includes first and second laterally adjacent pluralities ofsprocket teeth projecting outwardly from the sprocket wheel. The vehiclefurther includes an endless track supported by the frame. The endlesstrack passes around the at least one sprocket and has first, second, andthird pluralities of laterally adjacent track teeth that engage thefirst, second, and third pluralities of sprocket teeth, respectively.The at least one sprocket may consist of two sprockets. A portion of thetrack may be longitudinally, resiliently deformable and the firstplurality of sprocket teeth may only engage the third plurality of trackteeth when the track longitudinally deforms

Additional and/or alternative objects, features, aspects, and advantagesof the present invention will become apparent from the followingdescription, the accompanying drawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention as well as otherobjects and further features thereof, reference is made to the followingdescription which is to be used in conjunction with the accompanyingdrawings, where:

FIG. 1 is a side view of a snowmobile according to an embodiment of thepresent invention;

FIG. 2 is a perspective view of a drive sprocket of the snowmobileillustrated in FIG. 1;

FIG. 3 is a front cross-sectional view of the drive axle and drivesprockets, taken along the line 3-3 in FIG. 1;

FIGS. 4 and 5 are side views of the drive sprocket and track of thesnowmobile illustrated in FIG. 1;

FIG. 6 is a partial perspective view of the track of the snowmobileillustrated in FIG. 1;

FIG. 7 is a partial top view of the circumferential edge of the drivesprocket according to another embodiment of the present invention;

FIG. 8 is a partial top view of the circumferential edge of the drivesprocket according to yet another embodiment of the present invention;

FIGS. 9 and 10 are side views of one conventional drive sprocket andtrack;

FIG. 11 is a perspective view of a second conventional drive sprocket;

FIG. 12 is a front view of a plurality of conventional drive sprockets,like the sprocket illustrated in FIG. 11, incorporated into thepropulsion system of a snowmobile;

FIG. 13 is a partial exploded view of the propulsion system illustratedin FIG. 12;

FIG. 14 is a partial perspective view of another conventional drivesprocket;

FIG. 15 is an enlarged perspective view of the sprocket teeth of thedrive sprocket of FIG. 14; and

FIG. 16 is a partial top view of the circumferential edge of the drivesprocket of FIG. 14 illustrating the axially-extending sprocket teethand the radially-extending sprocket teeth.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

As illustrated in FIG. 1, a snowmobile 10 according to an embodiment ofthe present invention includes a frame 15 that supports a pair ofselectively steerable skis 20. An endless track 30 is supported by theframe 15 through a slide rail suspension system 40. The frame 15 alsosupports a straddle-type seat 50.

The snowmobile 10 includes a propulsion unit 60 (shown in phantom), suchas an internal combustion engine, that is operatively connected to theendless track 30 via a drive axle 70. A continuously variabletransmission (not shown) connects the propulsion unit 60 to the driveaxle 70. Two drive sprockets 80, as shown in FIG. 3 are mounted to thedrive axle 70 for common rotational movement about a drive sprocket axis85. As illustrated in FIGS. 2-6, each sprocket 80 includes three sets ofsprocket teeth 90, 100, 110 that engage three corresponding sets oftrack teeth 120, 130, 140 in the endless track 30 to provide tractionbetween the sprockets 80 and the endless track 30.

The drive sprocket 80 comprises a generally disc-shaped sprocket wheel150 that has an outer perimetrical surface 160 and two opposing axialsurfaces 170, 180. The sprocket wheel 150 has a central bore 190 throughwhich the drive axle 70 extends. The bore 190 and the drive axle 70 havemating hexagonal cross-sections that rotationally secure the sprocket 80to the drive axle 70. Alternative methods of rotationally securing thesprocket 80 to the drive axle 70 may also be used (e.g., a key andkeyway, square cross-sections, radial pins, etc.).

The sprocket teeth 100 comprise circumferentially-spaced teeth thatproject radially outwardly from the perimetrical surface 160. Thesprocket teeth 90, 110 comprise circumferentially-spaced teeth thatproject axially outwardly from the axial surfaces 170, 180,respectively. Because the sprocket teeth 110 are mirror images of thesprocket teeth 90, only the sprocket teeth 90 will be discussed indetail below. It is to be understood that the description of thesprocket teeth 90 applies equally to the sprocket teeth 110.

The sprocket wheel 150 and the sprocket teeth 90, 100, 110 areintegrally formed, for example by integral metal casting. To reduce theweight of the snowmobile 10, the sprocket 80 preferably comprises astrong, light material such as aluminum or plastic. Also, while thesprocket 80 is preferably made of plastic, it is contemplated that thesprocket 80 may be made of any other material including steel or acomposite material including aluminum. In addition, the sprocket 80could be made from a composite including carbon fibers. In other words,the exact composition of the sprocket 80 may be selected from a widevariety of substances without departing from the scope of the presentinvention. In addition, the sprocket teeth 90, 100, 110 may be formedseparately from the sprocket wheel 150 and subsequently rigidly fastened(via glue, rivets, welds, bolts, etc.) to the sprocket wheel 150.

As illustrated in FIGS. 4 and 5, the sprocket teeth 90, 100, 110 arepreferably radially aligned such that each sprocket tooth 90 is disposedat the same circumferential position as a corresponding one of each ofthe sets of sprocket teeth 100, 110. However, the sets of sprocket teeth90, 100, 110 may alternatively be out of phase with each other withoutdeparting from the scope of the present invention.

As illustrated in FIGS. 2, 4 and 5, the perimetrical surface 160 definessprocket valleys 200 between adjacent sprocket teeth 100. Theperimetrical surface 160 is generally cylindrically shaped such that thesprocket valleys 200 each have an arc-shaped surface. Each of thesprocket teeth 90 have radially outward surfaces 90 a that extendradially outwardly farther from the rotational axis 85 than the adjacentsprocket valleys 200.

Each sprocket tooth 90 includes a base portion 90 c connecting thesprocket wheel 150 to the tip portion 90 b. Notches 210 are formed onopposite circumferential sides of the base portion 90 c of each sprockettooth 90. The notches 210 delimit the transition point between the baseportion 90 c and the tip portion 90 b.

As illustrated in FIGS. 1 and 6, the endless track 30 comprises anendless flexible belt 220 with an inner side 220 a and an outer side 220b. The endless track 30 includes a plurality of lugs (or ribs) 230 thatproject from the outer side 220 b to give the endless track 30 tractionagainst the snow as the endless track 30 propels the snowmobile 10.

As illustrated in FIG. 6, the track teeth 130 are defined by a pluralityof longitudinally spaced holes 240 through the endless belt 220. Asillustrated in FIGS. 4 and 5, inner surfaces 130 a of the track teeth130 are defined by the inner side 220 a of the belt 220.

The endless track 30 also comprises a plurality of alignment cleats 250that are mounted onto the track teeth 130. As illustrated in FIGS. 4 and5, each cleat 250 includes a base portion 250 a and a cleat portion 250b. The base portion 250 a has a generally C-shaped cross-section thatwraps around the inner surface 130 a of one of the track teeth 130. Thecleat portion 250 b projects inwardly away from the inner side 220 a ofthe belt 220. The alignment cleats 250 preferably comprise a strong,light, stamped sheet of metal such as steel. As would be appreciated bythose skilled in the art, however, any other suitable material (e.g.,aluminum, etc.) may be used. Moreover, the cleats 250 need not bestamped from a metal sheet but may be cast or molded into theappropriate configuration.

Two sets of the track teeth 120,140 project inwardly from the inner side220 a of the endless belt 220. The track teeth 120 are longitudinallyspaced from each other around the inner side 220 a. The track teeth 140are also longitudinally spaced from each other around the inner side 220a. Track valleys 260 are defined by the inner side 220 a of the endlessbelt 220 between longitudinally adjacent pairs of the track teeth 120,140. The track teeth 120, 140 are positioned laterally adjacent to thetrack teeth 130 but are disposed on opposite lateral sides of the trackteeth 130. Each of the track teeth 130 longitudinally registers with onetooth from each of the sets of track teeth 120, 140 (i.e., teeth fromeach set of track teeth 120, 130, 140 are longitudinally aligned) in thepreferred example. Of course, if desired, the track teeth 120, 130, 140need not be longitudinally aligned. Offset track teeth 120, 130, 140 arealso considered to fall within the scope of the present invention.

The endless track 30 comprises a strong, flexible material such asrubber reinforced with fabric and metal. The endless belt 220 and trackteeth 120, 130, 140 are integrally formed with each other.Alternatively, any one or more of the track teeth 120, 130, 140 may beformed separately from the remaining components of the endless track 30and subsequently attached to the endless track 30 (via glue, bolts,rivets, etc.).

While only one lateral side of the endless track 30 has been describedin detail, it is to be understood that, as is shown in FIGS. 3 and 6,additional, laterally-offset sets of track teeth mirror the track teeth120, 130, 140. The additional track teeth engage the second sprocket 60.

Hereinafter, the engagement between the sprocket 80 and the endlesstrack 30 is described with specific reference to FIGS. 4 and 5. Thesprockets 380 and 480 described below engage the endless track 30 in asimilar manner.

During low-load operation of the snowmobile 10 (e.g., during lowacceleration, constant low speed use, coasting, etc.), successivesprocket teeth 90, 110 engage successive track teeth 120, 140,respectively. During this low-load engagement, the traction providedbetween the sprocket teeth 90, 110 on the two laterally spaced sprockets80 and track teeth 120, 140 is sufficient to prevent the endless track30 from slipping relative to the sprockets 80.

The sprocket 80 and track 30 reduce noise by reducing or eliminatingrattling contact between the alignment cleats 250 and the sprocket 80.As the sprocket 80 rotates, the outer surfaces 90 a of the sprocketteeth 90 register with and contact the track valleys 260. Similarly, theinner surfaces 130 a of the track teeth 130 and their surrounding cleatbases 250 a register with the sprocket valleys 200. However, because thesprocket valleys 200 are disposed radially inwardly on the sprocket 80relative to the outer surfaces 90 a and because the cleat base portions250 a are disposed at generally the same level (in a directionperpendicular to the inner side 220 a of the endless track 220) as thetrack valleys 260, the cleat base portions 250 a remain slightly spacedfrom the sprocket valleys 200. Consequently, the metal cleats 250 do notrattle against the sprocket 80 to generate noise.

In the illustrated embodiment, while sprocket tooth and valley heightdifferences are used to prevent the cleats 250 from rattling against thesprockets 80, various other dimensions may alternatively be altered toachieve the same result without departing from the scope of the presentinvention. For example, the track valleys 260 could be built up slightlyto space the cleats farther away from the sprocket valleys.Alternatively, the cleats could be disposed in depressions formed on theinner side 220 a of the endless belt 220 to create a height gap betweenthe cleats 250 and the track valleys 260.

As the sprocket 80 rotates, the cleat portions 250 b of the cleats 250extend into the notches 210 formed in adjacent ones of the sprocketteeth 120. If the cleat portions 250 b are longitudinally narrow enough,the cleat portions 250 b may simply extend into an open area formedbetween the notches 210 of adjacent sprocket teeth 120. Because thecircumferential width of the space formed between adjacent notches 210is larger than the longitudinal width of the cleat portions 250 b, thecleat portions 250 b do not typically contact the sprocket teeth 90,even when the track teeth 120, 140 deform slightly in its longitudinaldirection. However, if the endless track 30 and sprocket 80 begin tomisalign, the cleat portions 250 b contact the sprocket 80 to urge thetrack 30 back into alignment with the sprocket 80. Accordingly, unlessthe cleats 250 are realigning the endless track 30 and sprocket 80,cleat-to-sprocket rattling is reduced or eliminated altogether.

During low-load operation, the endless track 30 does not significantlylongitudinally deform and the track and sprocket teeth 90, 110, 120, 140provide sufficient traction between the sprockets 80 and the endlesstrack 30. Accordingly, the sprocket 80 and track 30 are designed so thatthe sprocket teeth 100 (and the cleat base portions 250 a that surroundthe sprocket teeth 100) do not contact or engage the track teeth 130. Ina circumferential direction of the sprocket 80, the sprocket teeth 100are slightly narrower than the sprocket teeth 90, 110. However, theengaging faces of the track teeth 120, 130, 140 are longitudinallyaligned. Consequently, when the sprocket teeth 90, 110 engage the trackteeth 120, 140, a slight circumferential gap is formed between themating faces of the sprocket teeth 100 and the track teeth 130 (and thecleat base portions 250 a). The cleat base portions 250 a do not,therefore, contact or rattle against the sprocket teeth 100.

As the load exerted on the endless track 30 by the sprocket 80increases, the sprocket and track teeth 90, 110, 120, 140 become lesscapable of handling the increased tractional load between the sprocket80 and the endless track 30. Simultaneously, the endless track 30deforms longitudinally. The longitudinal deformation of the endlesstrack 30 closes the gap between the cleat base portions 250 a (and thetrack teeth 130) and the sprocket teeth 100. The sprocket teeth 100,therefore, engage the cleat base portions 250 a and track teeth 130 toprovide additional sprocket-to-track traction.

While engagement between the sprocket teeth 100 and the track teeth 130causes the sprocket 80 to rattle against the cleat base portions 250 a,the high-load situations when the additional traction is requiredtypically occur when the snowmobile 10 is traveling slowly butaccelerating quickly. The slower rotational speed of the sprocket 80 inthis situation minimizes the increased noise caused by cleat 250rattling.

While in the illustrated embodiment, the sprocket teeth 100 selectivelyengage the track teeth 130 during high loads by reducing thecircumferential length of each sprocket tooth 100, the same effect maybe obtained by modifying various other components of the endless track30 and/or sprocket 80. For example, instead of circumferentialiynarrowing the sprocket teeth 100, the holes 240 in the endless track 30could be longitudinally widened slightly. Alternatively, the sprocketteeth 100 could be circumferentially shifted slightly relative to thesprocket teeth 90, 110 or the track teeth 130 could be longitudinallyshifted slightly relative to the track teeth 120, 140. Consequently, thesprocket teeth 100 would be slightly out of phase (in a trailingdirection) with the track teeth 130.

The sprocket 80 is designed to be used with a conventional track likethe track 1030 illustrated in FIGS. 9 and 10. The track 1030 includesall of the functional components of the endless track 30. However, if,as is discussed above, one of the track components is modified toachieve one of the objectives of the present invention, a specificallydesigned track would replace the conventional track 1030.

Furthermore, while in the illustrated embodiment, the sprocket teeth 100selectively engage the track teeth 130 only during high loads, suchselective engagement is not required to practice the present invention.For example, the sprocket and track teeth 90, 100, 110, 120, 130, 140may be positioned and sized such that all three sets of sprocket teeth90, 100, 110 simultaneously, continuously engage all three sets of trackteeth 120, 130, 140, respectively, to continuously provide increasedtraction between the sprocket 80 and the endless track 30.

As illustrated in FIG. 3, because the sprocket and track teeth 90, 100,110, 120, 130, 140 provide substantial traction between each sprocket 80and the endless track 30, only two sprockets 80 are required. Thisreduces the weight of the moving parts of the snowmobile 10 as comparedto conventional four sprocket arrangements (see, e.g., FIG. 12). Whiletwo sprockets 80 are used in the illustrated embodiment, greater orfewer sprockets 80 may alternatively be used. The precise number ofsprockets 80 that should be used to drive an endless track will bedictated by the tractional requirements of the specific tracked vehicle.Furthermore, a sprocket 80 may be used in conjunction with one or moreconventional sprockets such as the previously described sprockets 1010,1060 (see FIGS. 9, 10 and 11).

Variations of the drive sprocket 80 are illustrated in FIGS. 7 and 8.Like the sprocket 80, each sprocket 380 shown in FIG. 7 includes threesets of sprocket teeth 390, 400, 410 that engage three correspondingsets of track teeth 120, 130, 140 in the endless track 30 to providetraction between the sprockets 80 and the endless track 30. The sprocket380 has a similar construction to the drive sprocket 80. For the sake ofbrevity, the common components including the endless track 30 will notbe described in further detail. Reference is made to the descriptionabove.

The sprocket teeth 400 comprise circumferentially-spaced teeth thatproject radially outwardly from the perimetrical surface 160. Thesprocket teeth 390, 410 comprise circumferentially-spaced teeth thatproject axially outwardly from the axial surfaces 170, 180,respectively. The sprocket teeth 390 and 410 are substantially mirrorimages. The drive sprocket 480 is illustrated in FIG. 8, the sprocket480 differs from sprocket 380 in that one set of the axially-extendingteeth is missing.

Like the sprocket teeth 90, 100 and 110, the sprocket teeth 390, 400,410 are preferably radially aligned such that each sprocket tooth 390 isdisposed at the same circumferential position as a corresponding one ofeach of the sets of sprocket teeth 400, 410, as shown in FIG. 7. In theembodiment of FIG. 8, the sprocket teeth 390 are disposed at the samecircumferential position as the sprocket teeth 500.

The perimetrical surface 160 defines sprocket valleys 200 betweenadjacent sprocket teeth 400 or 500. Like the sprocket teeth 90, each ofthe sprocket teeth 390 has radially outward surfaces 390 a that extendradially outwardly farther from the rotational axis 85 than the adjacentsprocket valleys 200. Each sprocket tooth 390 includes a base portion390 c connecting the sprocket wheel 150 to the tip portion 390 b.Notches 391 are formed on opposite circumferential sides of the baseportion 390 c of each sprocket tooth 390. The notches 391 delimit thetransition point between the base portion 390 c and the tip portion 390b. Each tip portion 390 b includes a notch 392 formed therein. Thenotches 392 provide a valuable reduction in weight without sacrificingperformance.

The sprocket teeth 400 in FIG. 7 and sprocket teeth 500 in FIG. 8 havesimilar construction. The size of the teeth 500 are narrower whencompared to the width of the teeth 400 due to the reduced thickness ofthe sprocket 480. In the embodiments illustrated in FIGS. 7 and 8, theteeth 400 and teeth 500 have a width that is narrower than the teeth 390and/or teeth 410. With such an arrangement, the teeth 400 and the teeth500 can be formed on top of the sprocket teeth 390 and 410 rather thanon the circumferential side of the sprocket like the prior art. Withsuch a construction, the perimetrical surface 160 of the sprockets 380and 480 does not contact the endless track 30, which further reduces thegeneration of noise. The sprockets 380 and 480 engage the endless track30 in the same manner as described above in connection with sprocket 80.As shown in FIGS. 7 and 8, the sides of the teeth 500 may have a concavecurvature, which further reduces the weight of the sprocket.

While the present invention has been described and illustrated as beingembodied in a snowmobile 10, the present invention is not limited tosnowmobiles. Rather, the present invention is considered applicable tothe propulsion of endless tracks used on all types of tracked vehicles,including snow groomers, plows and muskeets.

Furthermore, Additional teeth may be provided on the sprocket 80, 380,480 and/or the endless track 30 that do not correspond to any of thesprocket or track teeth 90, 100, 110, 120, 130, 140. In other words, notevery tooth on the sprocket 80 and track 30 needs to be one of the teeth90, 100, 110, 120, 130, 140.

The foregoing illustrated embodiments are provided to illustrate thestructural and functional principles of the present invention and arenot intended to be limiting. To the contrary, the principles of thepresent invention are intended to encompass any and all changes,alterations and/or substitutions within the spirit and scope of thefollowing claims.

1. A vehicle comprising: a frame; a power plant supported by the frame;a sprocket operatively connected to the power plant, the sprocketcomprising: a sprocket wheel rotationally supported by the frame andoperatively connected to the power plant, the sprocket wheel having arotational axis, a perimetrical surface, and first and second axialsurfaces, a first plurality of sprocket teeth extending radiallyoutwardly from the perimetrical surface in spaced-apart relation, asecond plurality of sprocket teeth extending axially outwardly from thefirst axial surface in spaced-apart relation, and a third plurality ofsprocket teeth extending axially outwardly from the second axial surfacein spaced-apart relation; an endless track supported by the framepassing around and engaging the sprocket comprising: an outer side andan inner side, the track defining a plurality of holes therethrough, theportions of the track between the plurality of holes being a firstplurality of track teeth adapted to engage the first plurality ofsprocket teeth; a second plurality of track teeth projecting from theinner side of the endless track adapted to engage the second pluralityof sprocket teeth; and a plurality of ground-engaging lugs projectingfrom the outer side of the endless track, wherein, only when the secondplurality of track teeth deform under load exerted thereon by the secondplurality of sprocket teeth, does the first plurality of sprocket teethengage the first plurality of track teeth to supplement traction betweenthe sprocket and the endless track.
 2. The vehicle according to claim 1,wherein the endless track further comprises a third plurality of trackteeth projecting from the inner side of the endless track adapted toengage the third plurality of sprocket teeth.
 3. The vehicle accordingto claim 1, wherein each of the second and third pluralities of trackteeth are disposed laterally adjacent to each of the first plurality oftrack teeth, on opposite sides thereof.
 4. The vehicle according toclaim 1, wherein each of the first plurality of sprocket teeth, each ofthe second plurality of sprocket teeth, and each of third plurality ofsprocket teeth are axially aligned.
 5. The vehicle according to claim 1,wherein the endless track further comprises a plurality of cleats, eachcleat including a base portion secured to one of the first plurality oftrack teeth and at least one cleat portion projecting from the baseportion away from the inner side of the endless track.
 6. The vehicleaccording to claim 5, wherein when the second plurality of track teethdo not deform under load exerted thereon by the second plurality ofsprocket teeth, the base portions of the cleats do not contact the firstplurality of sprocket teeth.
 7. The vehicle according to claim 5,wherein only when the second plurality of track teeth deform under loadexerted thereon by the second plurality of sprocket teeth, does thefirst plurality of sprocket teeth engage the cleats to enhance tractionbetween the sprocket and the endless track.
 8. The vehicle according toclaim 5, wherein each of the second plurality of sprocket teeth has atleast one notch formed therein.
 9. The vehicle according to claim 8,wherein each of the second plurality of sprocket teeth has a baseportion and a tip portion, wherein the at least one notch is formed onone side of the base portion of the second plurality of sprocket teethsuch that the cleat portion projecting from the base portion of thecleat enters therein.